THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47 St., New York, N.Y. 10017

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Design and Construction of the First Commercial Cheng Cycle Series 7 Plant

J. LLOYO JONES, DR. CHUNG-NAN CHANG, DR. RAMARAO V. DIGUMARTHI, DR. WILLIAM M. CONLON

International Power Technology Palo Alto, Calif.

ABSTRACT on the Cheng Cycle. The HRSG unit consists of:

A description is given of the Cheng Cycle Engine a superheater, located immediately downstream of and its application to cogeneration based upon the the turbine exhaust diffuser section, to raise first commercial plant. The paper covers a description the temperature of the injection steam to as high of the plant and its components, unique design features, a value as possible before injection. This the automatic control system and the plant operational temperature elevation reduces the amount of features. Initial operating performance and NOx additional fuel that needs to be supplied to the emission characteristics are cited. to raise the temperature of the steam to turbine inlet temperature, and thus enhances INTRODUCTION the engine rate.

The Cheng Cycle Series 7 Engine represents an a secondary combustor, located immediately down- innovative new concept in industrial gas turbines. A stream of the superheater, followed by a combustion detailed discussion of the Cheng Cycle, the potential duct section. This secondary combustion provides gains in power and efficiency that its application for the production of additional steam either would yield for a number of gas turbine engines, and for increased power generation or for process, an example of the performance improvements it offers depending upon the desired operating condition. in cogeneration applications is given in Reference 1. Three units were installed in two cogeneration an evaporator, located immediately downstream of plants by International Power Technology, Inc. in the combustion duct, for steam generation. 1984. Both plants completed acceptance tests in December 1984, and were in commercial operation in an economizer, located downstream of the steam January, 1985. Two units comprise a single plant generator, and at Sunkist Growers, Inc., in Ontario, California. The third unit, the first to be placed in operation, a feedwater heater. is located at the California State University at San Jose. This paper describes briefly the Cheng The operating regime of the Cheng Cycle Series 7 Engine Cycle Engine concept and characteristics and the Cogeneration application is illustrated in Fig. 2. San Jose State University cogeneration plant compo- Point 2 indicates the power generated by the basic nents, design features, operation and control system gas turbine driving the generator with no steam characteristics and initial performance levels. injection, and the amount of steam for process generated by the HRSG with no heat added to the exhaust gas by THE CHENG CYCLE SERIES 7 ENGINE COGENERATION SYSTEM the secondary combustor. Under this condition, the superheater operates dry. As steam is directed from An illustration of the Cheng Cycle Series 7 process to the gas turbine, the power output of the Engine in a cogeneration plant installation is given turbine and of the generator increases along line 2-1, in Fig. 1. The Cheng Cycle Series 7 Engine consists which represents a constant turbine inlet temperature of an Allison 501-KH gas turbine in combination with of 1895 degF (1308 degK) the highest allowable firing a heat recovery steam generator (HRSG) that is closely temperature for continuous duty. At point 1 all of matched to assure high cycle efficiency. Steam from the steam generated by the gas turbine exhaust heat the HRSG is injected into the gas turbine combustion energy is injected into the gas turbine and none is region to increase the power output of the basic available for process. Use of the secondary combustor engine. The KH version of the 501 engine incorporates expands the operating regime of the cogeneration system modifications by Allison specifically for operation from line 1-2 to include the entire area A . Line 3-4

Presented at the 1985 Beijing International Gas Turbine Symposium and Exposition Beijing, People’s Republic of China — September 1-7, 1985 STEAM TO ‘PROCESS

-

GENERATING SET 4 HEAT RECOVERY STEAM GENERATOR

CHENG CYCLE SERIES 7-COGEN PLANT LAYOUT Fig. 1

by derating the gas turbine operation to lower turbine inlet temperatures. In the first commercial installa- tion at the California State University in San Jose, initial operation is being limited to a turbine inlet temperature of 1800 degF (1255 degK and a secondary combustion firing rate to provide a temperature of 1400 degF (1033 degK) entering the evaporator. The operating regimes for this plant are defined by the dotted lines in Fig. 2.

THE FIRST COMMERCIAL PLANT

The first commercial plant completed its formal acceptance tests in December, 1984. The plant is an indoor installation located in a previously unused TURBINE DERATING & | section of the existing power house at the University SECONDARY COMBUSTION | that had originally been planned for expansion of | the existing plant. A sectional elevation view of the | plant is given in Fig. 3, where it may be seen that | , , | | I. | | | | | major components are on a ground level operating floor, 0 1.0 20 3.0 40 with auxiliary equipment in a basement. The primary PROCESS THERMAL OUTPUT fuel is natural gas, which is supplied by the local MILLION Btu/Hour utility at a of 100 to 150 psig. A rotary type gas compressor boosts the pressure to 300+ psig CHENG CYCLE SERIES 7-COGEN required to supply the gas turbine. The liquid fuel OPERATING REGIME is pumped from underground tanks to an elevated head tank from which it is drawn by a shaft driven fuel Fig. 2 pump on the gas turbine. Engine air is drawn from above through ducting into a plenum within the gas turbine-generator set enclosure. The ducting extends represents firing of the secondary combustor to obtain down to the basement level and outside to an open a temperature of 1600 degF (1144 degK entering the subsurface areaway. A self-cleaning filter and an evaporator. evaporative cooler through which the engine air is In most cogeneration installations, the process drawn are located in this areaway. Cooling air for steam demand is given highest priority. for example, If the generator, gearbox and gas turbine is drawn into the process steam demand were 20 million BTU/hour, the enclosure through a silencer/filter on top of the the electrical power output would be limited to about enclosure, circulated separately through the generator 4 megawatts. If a higher power output were required, and through the remainder of the enclosure and exhausted firing of the secondary combustor would provide through two ducts extending through the roof. additional steam for injection into the gas turbine Plan views of both the operating floor level and to permit the electrical power to be raised to any the basement level are shown in Figs. 4 and 5. The level up to the maximum of 6 megawatts, while maintain- engine inlet air ducting extension may be seen in these ing the process steam flow of 20 million BTU/hour. Figures and the filter and cooler units may be seen in Alternately, if the process steam demand increased, Fig. 5. The rather abrupt expansion duct section firing of the secondary combustor would permit the joining the gas turbine exhaust nozzle covering to the generation of more steam for process, while maintaining superheater is of internally insulated double wall the electrical power output of 4 megawatts. Obviously construction and is fitted with a series of turning combinations exist to permit operation anywhere within vanes to avoid flow separation and maintain the pressure the area A. Operation in areas B and C are possible

2 Fig. 3 ELEVATION VIEW, COGENERATION PLANT PLAN VIEW, COGENERATION PLANT, OPERATING FLOOR LEVEL.

Fig. 5 PLAN VIEW, COGENERATION PLANT, BASEMENT LEVEL. drop of the exhaust gas/steam mixture at the lowest boilers will be placed on standby and used to provide practical value. Photographs taken during the final steam during periods when the cogeneration plant is construction stages and showing the generator set down for maintenance or overhaul. enclosure and HRSG are presented in Figs. 6 and 7. Electrical power is generated at 12.47 KV, the While the gas turbine generator set and the HRSG were voltage of the main electrical bus, and the generator designed to keep the external noise levels to within is tied through a protective breaker directly to the acceptable values, the plant control room is sound bus. Electrical energy is supplied to serve the proofed and air conditioned. Interconnecting power University needs, and excess is exported to the local and instrumentation wiring from the generator set, utility (Pacific Gas and Electric Company) grid. If the HRSG and auxiliary equipment is run in trays the University electric demand exceeds the output of beneath the operating floor, leaving a relatively the cogeneration plant, the shortfall can be imported free and uncluttered area around the unit. Cooling from the utility grid. In case the utility grid is fans for the compressed natural gas and for the down, the cogeneration plant can supply the University generator, gear box and gas turbine lubricating oil as an isolated grid. draw air through heat exchanger units and exhaust The cogeneration plant was installed at no cost into an open cooling tower area. (See Fig. 5 - The to the University. It is owned by a third party and cooling towers are used in conjunction with water is operated for the owner by IPT Energy Management chillers which provide for space cooling on the Corporation. The University has an option to purchase campus.) the plant. The prime contractor and Architect-Engineer Steam is generated by the HRSG at a drum pressure was Ebasco Services, Inc. of Santa Ana. The developer 6 2 of 205 psig (1.413 x 10 Newtons/m This pressure was IPT-Catalyst, and International Power Technology, is dictated by the need to provide steam for injection Inc., patent holder for the Cheng Cycle, furnished into the gas turbine at a pressure of approximately the Generator set and the HRSG, which in turn were 170-180 psig (1.172 x 106-1.241 x 106 Newtons/m2 built by Valley Detroit Diesel Allison and the Deltak allowing for pressure drops through the line, flow Corporation. control valve and the superheater. Steam is supplied to the University's steam header at a pressure of DESIGN FEATURES 50 to 100 psig (3.447 x 105 to 6.894 x 105). The steam supplied to the University is used for space The Allison 501-KH gas turbine is a modification heating and cooling in buildings throughout the of the 501-KB5 to operate with steam injection. Two campus. An existing underground steam distribution annular steam manifolds are incorporated in the system is used for heating. In summertime, steam is combustor section casing. The casing, in turn, has used as the energy source for water chillers. The holes for steam admittance into the combustion section chilled water is distributed to the University which is comprised of six cylindrical combustion cans building's air conditioning units. Existing fired arranged in an annular ring. Superheated steam for

3 Fig. 6 GAS TURBINE GENERATOR ENCLOSURE DURING Fig. 8 GAS TURBINE STEAM INJECTION LINES AND MANIFOLD CONSTRUCTION.

rises and the steam flow rate is regulated by the injection steam control valve. This concept allows very smooth starts of the Cheng Cycle operation. The steam drum, as may be noted in Fig. 4, is oversized to provide for greater stability in the water level - a necessity because of the possible rapid and large changes in steam demand as the gas turbine engine responds to sudden electrical demand changes possibly coupled with changes in process steam demand. The injected steam acts very much like water injection to reduce the NOx production in the gas turbine combustors. The diversion of steam from the downstream to the upstream manifold provides the possibility to enhance the NOx suppression at the lower steam injection rates. While operation of the San Jose State University plant at the present time calls for firing of the secondary combustor to only 1400 degF (1033 degK) the system was designed for firing to 1600 degF (1144 degK) This was done to allow for possible future increases in steam demand and because 1600 degF (1144 degK) was Fig. 7 GAS TURBINE GENERATOR SET AND HRSG DURING adapted as a standard design temperature for the Cheng CONSTRUCTION. Cycle Series 7 Cogeneration unit. Recognizing the large amount of water vapor in the exhaust stream, injection is bought into the gas turbine section of special consideration had to be given to the radiation the generation set enclosure by two 6-inch diameter heating from the secondary combustor flame zone to the pipes. Each pipe is fitted with a tee section first rows of tubing in the evaporator. Accommodation to this high heating load (radiation and convection) containing a splitter plate and carried to flanged connections on the annular manifolds. There are two was made by leaving the first row of tubes bare of fins and providing stainless fins in the second row flanged connections at 180 deg F on each manifold. The photograph in Fig. 8 shows the two annular of tubes. Concern about the possible deleterious effects manifolds about the combustion section and one of the two steam lines running to each. of solids carried through the turbine by the injected A portion of the plant piping and instrumentation steam caused special attention to be given to the diagram is shown in Fig. 9. Upon startup of the quality of the feedwater. A large percentage of makeup water must be added on a continuous basis system, the gas turbine is brought up to speed at zero load. Once at speed the gas turbine is then because the steam injected into the gas turbine is The carry over from the drum to the loaded to its basic load. As the drum begins steaming, not recovered. steam begins flowing to the engine as the drum pressure steam was held to 0.05%, and because the steam is

4 I

GENERATOR

Fig. 9 PIPING AND INSTRUMENTATION DIAGRAM - STEAM AND FEED WATER

TERMINAL CABINET MCC I ALL AROUND l- f SEE DRAWING 1

Fig 10. CONTROL ROOM LAYOUT superheated to over 900 degF (755 degK) in the super- (TCM) is shown in Fig. 11. The plant is fully automated heater, it is expected that no water droplets will ever and is capable of automatic operation with periodic reach the gasturbine. Because the gas turbine will be monitoring by personnel normally engaged in other in operation in excess of 8000 hours per year and a activities in the power plant building. The automatic large amount of steam will be injected per year, special control system was supplied by IPT and was developed treatment of the feed water was undertaken to provide using Bailey Network 90 hardware components. The first a margin of safety. The raw water at the site contains TCM unit houses an annunciator panel and critical total dissolved solids (TDS) in the amount of some 520 operating and safety system parameters. The second TCM ppm, and total hardness (as CaCO2) of 400. Reverse unit provides analog displays of the generator and bus osmosis and softener units were provided to bring the operating characteristics as well as protective relays makeup water total hardness to less than 0.05 and the and the gas turbine programmable controller. The third TDS down to 40 ppm. A continuous blowdown is utilized TCM unit contains electrical metering equipment (Jem to keep the Drum TDS concentration at a relatively low meters) for billing purposes as well as the electrical level. synchronizing equipment and the gas turbine governor. The digital Operator Interface Units supplied by CONTROL IPT provide upon call-up any information that appears on the TCM panels. In addition it controls the HRSG The layout of the control room is shown in Fig. 10. operation, including the control valve for the gas A photograph showing the screens for the Operator turbine injection (or Cheng Cycle) steam. Upon call-up Interface Units (OIU) and the Turbine Control Modules it provides status information for the HRSG system and

5 28DEC84 FRIDAY 9B PLANT PERFORMANCE S1234 67 11:38:39 s*

----a .e.“.-.Y--m .-..-“-..s :ffi.v~--“.------L “-2

,...... rn._...... “...... _...... I< .39 9:59 10: 19 10.39 10.59 11:19 I

Fig. 12a EXAMPLE OIU DISPLAY PRINTOUT

Fig. 11 OPERATOR INTERFACE UNIT DISPLAYS AND TURBINE CONTROL MODULES.

all balance of plant equipment. The operator can, 1985, is undergoing adjustments and minor modifications therefore, call-up on the OIU the operating status of of various components as time permits to tune the plant any element of the entire plant and the displays performance to the peak design levels. include a complete 26 hour history of all parameters. Emission measurements were taken at a turbine The OIU provides logging of all process steam production inlet temperature of 1800 degF (1255 degK) for plant and as back-up to the Jem meters, all electric power permitting, since the initial planned operation is at production. Either of the two OIU's is sufficient this temperature. The NOx emissions were measured for plant operation and data logging. The second unit to be about 10 ppm of dry flow (corrected to 15% 02) is for redundancy to assure continuous control and or about 70 lb/day, for a power production rate of has data logging. Each of the OIU's have a separate 5370 kw and for process steam ranging from 0 lbs/hr printer for continuous logging of data by periodic to 25,000 lb/hr by firing of the secondary combustor. printout. Examples of printer records for plant performance, turbine performance, turbine critical parameters and HRSG parameters (taken during the plant REFERENCE test operations) are shown in Fig. 12. There are a total of some eighty displays programmed in the OIU's 1. Jones, J.L., Flynn, B.R. and Strother, J.R., "Operating Flexibility and Economic Benefits of a INITIAL PERFORMANCE AND EMISSIONS Dual-Fluid Cycle 501-KB Gas Turbine Engine in Cogeneration Applications", ASME paper 82-GT-298, 1982. The Cheng Cycle system is a dynamically coupled system consisting of the heat recovery steam generator (HRSG) and the combustion turbine generator (CTG). The regenerative nature of the injected superheated steam is the key coupling link between the performance of the HRSG and the performance of the CTG. This interdependence allows all components of the system to be operating at their optimal levels, but requires a rapid response control system. Typical performance is shown in Fig. 13, where it may be seen that the power output was 5321 kw at generator terminals with a turbine inlet temperature of 1879 degF (1299 degK) At this operating condition 19.84 lb/hr (8999.4 kg/hr) of super heated steam was being injected and 49 mbtu/hr of natural gas fuel was being consumed. This performance corresponds to a generator power heat rate of 9210 btu/kwh or power generation efficiency of 37%. The performance data given herein are from initial operation in December, 1984. The plant, while in production operation in 28DEC84 FRIDAY 2B TURB PERFORMANCE S1234 67 11:37:39 28DEC84 FRIDAY 2A TURBINE CRIT PAR S1234 67 11 36 43

PK-200 DRUM FIK-204 MAX PRESS SET POINT INJECTION STEAM PSIG - 300. KW --7000 II OEGF-2000 II % --100 KLB/HR - 25.0 < 23 00 -- 1760. >-< 1722. 88.0 >-< 86 2 88.1 >-< 86.2 _-

181.8 H 181.8

-- 11 90>-

-0.00 -000 COTK 0% LOCAL AUTO 83% LOCAL

Fig. 12 b EXAMPLE OIU DISPLAY PRINTOUT Fig. 12c EXAMPLE OIU DISPLAY PRINTOUT

29DEC84 SATURDAY 4A TURBINE CRIT PAR S1234567 11:17:59

28DEC84 FRIDAY 4A HRSG CRITICAL PAR S1234 67 11:39:37

JR-100 Ill GENERATOR KW 5321.3 KW 6000.0

FR-204 INJECT l STEAM FLOW 19.84 KLB/HR ’ 0.00 :18 9.38 9:58 10: 18 10:38 10:58 I I I

FIK-212 LIK-202 STEAM FUEL VALVE CTRL DRUM LEVEL % --100. "H2O - 11.0

-< 71.7 66.3 >- 182.4 >-< 182.4 -- - -1.15 >-< -2.00

_-

--8.69 - -11. AUTO 100% LOCAL AUTO 37% LOCAL

Fig. 12d EXAMPLE OIU DISPLAY PRINTOUT Fig. 13 INITIAL PERFORMANCE